Prediction of wear-resistant thin diffusive coatings

Friction and wear process are investigated using experimental data and mathematical modeling of the specimen contact interaction. To study the wear in the system, ‘a rigid punch—thin coating—elastic base’, a mathematic statement of the problem was formulated. The integral equations were obtained and the solutions to the problems for punches, containing parabolic and wedge-shaped profiles, and also with a flattened basis were constructed. New regularities of deformation and wear of thin coatings on solids were obtained. The methods for crack growth resistance calculations in the coatings allow us to predict by the physicochemical, tribotechnical and geometrical characteristics the coatings life-time, which is proved experimentally on chromium-based coatings applied on carbon steels.     

Synthesis of carbon nanostructures by arc evaporation of graphite rods with Co-Ni and YNi2 catalysts

Yields of single-walled carbon nanotubes (SWNTs) produced from electric arc evaporation of graphite electrodes with 3Co/Ni and YNi₂ catalysts differ substantially. For instance, with YNi₂ catalyst, the SWNT yield is ∼30-50 wt.% in ‘collar’ soot and ∼10-15 wt.% in ‘wall’ soot, while with 3Co/Ni catalyst, the yields are ∼15-20 wt.% and 2-3 wt.%, respectively. According to Raman spectroscopy data, the average dimension of SWNTs is ∼1.2 nm for 3Co/Ni and ∼1.4 nm for YNi₂ catalyst. Optimum conditions for synthesis also differ for catalysts compared; namely, for 3Co/Ni: current intensity is 93 A, helium pressure is 650 Torr, the electrode gap is 2.5-3 mm; for YNi₂: current intensity is 98 A, helium pressure is 500 Torr, the electrode gap is 1-2 mm.     

Two-dimensional simulations of amplification of space charge waves in a strained Si/SiGe heterostructure at 77 K

We theoretically investigated the propagation and amplification of space charge waves on the surface of a strained Si/SiGe heterostructure at 77 K, using the negative differential conductance phenomenon. In this work, we also have done a comparison between the n-GaAs thin film and strained Si/SiGe heterostructure with respect to the propagation of space charge waves. We have obtained results in 2D of propagation and amplification of space charge waves in a strained Si/SiGe heterostructure until for frequencies f<40 GHz.     

Modification of poly(ethylene terephthalate) surface with attached dextran macromolecules

BACKGROUND: Peroxidation of a poly(ethylene terephthalate) (PET) surface clears the path to the formation of biospecific polymeric layers on it. The goal of this work was the modification of a PET surface with oligoperoxides with further grafting of dextran macromolecules to this peroxidated surface. RESULTS: Novel oligoperoxides with a good affinity to PET were synthesized. They are capable of attaching to the PET surface, due to the decomposition of peroxide groups via the formation of free radicals. The alterations in surface energy and its components as a result of surface modification as well as changes in topography of the PET surface were determined. The degree of modification of the PET surface can reach 68% and depends on the following: the method of oligoperoxide and dextran deposition; the concentration of both oligoperoxide and dextran in the initial solution; and the temperature at which the modification is carried out. CONCLUSION: A new method of PET surface activation has been developed. The attachment of dextran macromolecules to modified PET surfaces is confirmed. Copyright © 2009 Society of Chemical Industry     

Crosslinking agents of unsaturated polymers: evaluation of the agent efficiency

We have performed a comparison of efficacy of several curing agents. We have synthesized curing agents with C=C-bonds of allylic, acrylic or peroxide group type, as derivatives of pyromellitic acid: diallylic ester (I), tetraallylic ester (II), di-(2-methacryloyloxyethyl)-pyromellitate (III), tetra-(2-methacryloyloxyethyl)pyromellitate (IV), ditert-butylperoxypyromellitate (V) and tetratert-butylperoxypyromellitate (VI). The possibility to use these agents for curing an unsaturated film-forming copolymer which contains polybutadiene fragments was investigated. The unsaturated curing agents (I–IV) are able to form crosslinked copolymers in the presence of peroxide initiators such as benzoyl peroxide. The gelation process orders as well as the values of the effective activation energies for all curing agents studied have been determined. In the presence of curing agents of methacrylic type (III–IV) the crosslinking proceeds more rapidly than in the presence of allylic esters. Unsaturated curing agents containing carboxylic groups (I, III) promote faster formation of three-dimensional structures than tetra-substituted derivatives of pyromellitic acid. For curing agents of the peroxide type the inverse relation is observed. The hardness of films obtained using carboxylic curing agents is higher than for noncarboxylic ones. Films obtained in the presence of unsaturated curing agents exhibit higher hardness than those obtained in the presence of peroxide agents. Electronic Publication     

Formation of water-impermeable crust on sand surface using biocement

This paper examines the feasibility of using calcium-based biocement to form an impermeable crust on top of a sand layer. The biocement used was a mixture of calcium salt, urea, and bacterial suspension, which hydrolyzed urea with production of carbonate and an increase of the pH level. Applying 0.6 g of Ca per cm² of sand surface, the permeability of the biocemented sand can be reduced from 10⁻⁴ m/s to 1.6·10⁻⁷ m/s (or 14 mm/day) due to formation of the crust on sand surface. The rupture modulus (maximum bending stress) of the crust was 35.9 MPa, which is comparable with that of limestone. The formation of a water-impermeable and high strength crust layer on sand surface could be useful for the construction of aquaculture ponds in sand, stabilization of the sand dunes, dust fixation in the desert areas, and sealing of the channels and reservoirs in sandy soil.     

Retardation of nanoparticles growth by doping

The process of doping of CdS nanoparticles with Mn during colloidal synthesis is analyzed by EPR and optical studies. Analysis of EPR results demonstrated that Mn²⁺ ions are successfully incorporated into the nanoparticles and occupy the crystal sites both in the bulk of a NP and near the surface of a NP. Optical absorption measurements revealed the retardation of absorption edge shift during the growth for Mn-doped CdS NPs as compared to the undoped CdS NPs. It was concluded that the presence of Mn in the solution leads to the inhibition of NPs growth.     

One-pot synthesis of carbon nanotubes from renewable resource: cellulose acetate

In the present work, we report for the first time one-pot synthesis of carbon nanotubes (CNTs) by pyrolysis of cellulose acetate (CA) cross-linked with polyisocyanate in the fumed silica template. NiCl₂ was chosen as precatalyst for CNT growth. The diameter of CNTs is 24–38 nm and their wall thickness is 9–11 nm. The main role in the formation of CNTs by the pyrolysis of CA may be attributed to combination of closed macropores in the template formed by evolved CO₂ during cross-linking reaction and mesopores formed by silica particles. The macropores acted as microreactors while the mesopores templated catalytic nanoparticles. The importance of this method for CNT synthesis reported here consists of the utilization of readily available renewable resource—CA. Moreover the method does not require preliminary synthesis of catalyst, it is technologically simple (can be performed in the conventional tube furnace), and hence it is energetically efficient.     

Mn oxide coated catalytic membranes for a hybrid ozonation-membrane filtration: Comparison of Ti, Fe and Mn oxide coated membranes for water quality

In this study the performance of catalytic membranes in a hybrid ozonation-ceramic membrane filtration system was investigated. The catalytic membranes were produced by coating commercial ceramic ultrafiltration membranes with manganese or iron oxide nanoparticles using a layer-by-layer self-assembly technique. A commercial membrane with a titanium oxide filtration layer was also evaluated. The performance of the coated and uncoated membranes was evaluated using water from a borderline eutrophic lake. The permeate flux and removal of the organic matter was found to depend on the type of the metal oxide present on the membrane surface. The performance of the manganese oxide coated membrane was superior to that of the other membranes tested, showing the fastest recovery in permeate flux when ozone was applied and the greatest reduction in the total organic carbon (TOC) in the permeate. The removal of trihalomethanes (THMs) and haloacetic acids (HAAs) precursors using the membrane coated 20 times with manganese oxide nanoparticles was significantly better than that for the membranes coated with 30 or 40 times with manganese oxide nanoparticles or 40 times with iron oxide nanoparticles.